Dental compositions for endodontic purposes are desired to approach natural tooth structure with regard to physical properties and biocompatibility. Moreover, good handling properties are also desired. Accordingly, a great effort is documented by the prior art directed to the development of dental compositions for endodontic purposes, which have improved properties with regard to physical properties, biocompatibility, and handling properties.
In the case of a dental root canal sealing composition, the main objective is to achieve a high degree of tightness of the root canal filling. The quality of the root canal filling directly depends on the shrinkage upon setting and the solubility of the material used, as these properties are decisive for the impermeability of the treated root canal.
Moreover, a low viscosity of the composition is required in order to allow penetration of the composition into the dentin of the root canal and in order to facilitate the complete filling of the root canal including any cavities which could not be accessed by a high viscosity composition with insufficient flow properties. Moreover, in order to maintain a tight seal, the dental root canal sealing composition should have good adhesion to hard dental structure including dentin.
Dental compositions selected from a root canal sealing composition and a pulp capping composition are subject to additional requirements in that the cured product is required to have a high radioopacity. The contrast of the material in the root canal as observed by x-ray diagnostic methods permits conclusions regarding the quality of the filling. Accordingly, a particulate filler having high radioopacity is incorporated into the composition. Suitable filler materials have a high density and are prone to settle out from the dental composition during storage which gives rise to a stability problem of the composition which is aggravated when the viscosity of the composition is low. Therefore, a dilemma exists between to the viscosity of the composition and the storage stability of the composition. Furthermore, the storage stability may also be limited in case of precipitation of solid components dissolved or dispersed in the dental composition.
Moreover, dental compositions selected from a root canal sealing composition and a pulp capping composition that the composition are required to be curable in the absence of light. In order to be able to cure a root canal sealing composition or pulp capping composition in the absence of light, the composition is cured by a thermal curing mechanism which may involve step growth polymerizing epoxide precursor compounds such as bisphenol-A diglycidylether or bisphenol-F diglycidylether with amine precursors. Bisphenol-A diglycidyl ether or bisphenol-F diglycidylether provide an excellent combination of properties for the purpose of a dental compositions including a favourable gel time in step-growth polymerizations with a diamine or polyamine. Moreover, favourable mechanical properties of the cured compositions while the viscosity of the uncured compositions may be adjusted to be comparably low, and a low shrinkage of the compositions upon curing are reasons for the widespread use of bisphenol-A or bisphenol-F diglycidylether based materials in the dental field.
From the prior art, a dental root canal sealer is known which consists of a paste-paste system AH Plus®. A first paste contains a diepoxide, calcium tungstate, zirconium oxide, aerosil, and a pigment. A second paste contains 1-adamantane amine, N,N′-dibenzyl-5-oxa-nonandiamine-1,9, TCD-diamine, calcium tungstate, zirconium oxide, aerosil, silicone oil. The composition cures in a step growth polyaddition reaction into a thermoplastic material. The polyaddition reaction of AH Plus® requires several hours whereby the gel time is about 16 hours.
Bisphenol-A and also bisphenol-F are known endocrine disrupters which can mimic estrogen and may lead to negative health effects. In particular, bisphenol A mimics the structure and function of the hormone estradiol with the ability to bind to and activate the same estrogen receptor as the natural hormone. Based on the functional relevance of bisphenol-A it is considered that bisphenol-A might contribute to the development of breast cancer. Accordingly, regulatory bodies might determine safety levels of bisphenol-A for humans so that the use of bisphenol-A based materials containing bisphenol A in a dental composition cannot be continued in the future.
At present, any of the commercially available root canal sealers based on epoxide-amine chemistry contain bisphenol-A diglycidylether (DGEBA): AH Plus® (DENTSPLY), AH 26 (DENTSPLY), Asphaline® (Alfred Becht GmbH), Acroseal® (Septodont), Adseal® (META BIOMED), Perma Evolution® (META BIOMED), EZ-Fill® (Essential Dental Systems).
WO 2013/120610 discloses a curable filler material mixture, comprising an epoxy as component (a), an amine as component (b), and a quaternary ammonium salt as component (c). The mixture contains a single epoxy as component (a), which may be resorcinol diglycidyl ether.